QPR failed to build on a first league win of the season at Gillingham on Friday despite a succession of second-half chances and are yet to win at home in the league.
United were without the services of striker Barry Hayles after he completed a move to Millwall for a nominal fee earlier in the day while Rangers forward Paul Furlong was also absent to be at the hospital bedside of his young son, who was injured in an accident this morning.
The visitors made a bright start and could have been ahead in the seventh minute but Alan Quinn could not quite deflect Ashley Ward's low cross from a throw-in on target.
Yet a catalogue of errors at the back cost the home side dearly in the 17th minute.
QPR failed to clear their lines calamitously and Quinn was able to cross for Jon Harley to flick back to Andy Gray, who made no mistake with a close-range finish.
Rangers then wasted two glorious chances to draw level in the space of two minutes, with Marcus Bean first putting a free header wide from a wicked Gino Padula corner on 25 minutes.
But Jamie Cureton's miss from six yards was perhaps worse after Lee Cook's mis-hit from a fabulous Martin Rowlands cross found him all alone only for the striker to make a hash of his finish.
Ashley Ward fashioned himself a chance out of nothing at the other end with a neat turn and shot, forcing Georges Santos into a full-stretch goalline clearance.
More confusion in the Rangers defence allowed Ward another shot on goal which deflected wide before Cook's deflected shot struck the United crossbar as the half wound down.
Harley could have doubled the lead shortly after the restart when Gray exchanged passes with Ward before crossing dangerously from the right, but he could not stretch far enough.
Rangers boss Ian Holloway rolled the dice by sending on Marc Bircham, Kevin McLeod and Matthew Rose just after the hour but it was United who threatened, Ward drawing a save from goalkeeper Chris Day.
Finally the home side began to apply the pressure but they could not find the finish in front of goal, with Santos and Kevin Gallen getting in each other's way and Bircham flashing a shot wide.
The nerves of the travelling fans were tested when the referee's assistant announced four minutes of injury-time but Rangers failed to capitalise.